The present invention relates to a video signal recording/reproducing apparatus, and more particularly to a video signal recording/reproducing apparatus having an electronic editing function.
In producing a program using a video signal recording/reproducing apparatus, particularly in the fields of broadcasting, advertising and education tape editing is an important, and sometimes indispensable work. In present video signal recording/reproducing apparatus for business use, it is typical to use a rotary head type video tape recorder (VTR) for effecting data recording/reproducing on a magnetic tape by video heads provided on the circumference of a rotary drum. Most of these VTRs have an editing function.
The editing operation in a video tape recorder has been called "electronic Edit". This electronic editing operation is carried out in principle by erasing portions of video and audio signals, which have already been recorded on a magnetic tape, and then recording new video and audio signals on the erased region of the magnetic tape.
If the editing is performed as described above, discontinuity of signals takes place principally before and after the editing start point. In particular, phase discontinuity of the video signals causes disturbance of synchronization and deteriorates the quality of a video image. In order to reduce the phase discontinuity that is caused editing, business using VTRs having the editing function use a method to servo-control the rotation phase of the VTRs rotary drum so that the phase of a vertical synchronous signal of video signals reproduced by a recording head during the reproducing period before the editing start point substantially coincides with the phase of a vertical synchronous signal of the input video signals to be recorded during editing.
The timing of the video signals reproduced by the recording heads indicates the rotating phase of the recording heads. If the rotation phase of the rotary drum is servo-controlled so that phases of the vertical synchronous signals from video signals reproduced by the recording heads during the reproducing period before the editing start point become almost the same as that of the vertical synchronous signals separated from input video signals, the phases of signals recorded on a magnetic tape before the editing start point and these of signals newly recorded after the editing start point become substantially the same. Therefore, it becomes possible to minimize the disturbance of video images before and after the editing start point during reproduction.
The method described above is effective on a VTR that is reproducing signals using the recording heads. However, this method is not applicable to such a VTR that is not able to reproduce signals with the recording heads, that is, a type of VTR which has recording heads for recording only and has another head for reproducing. this is because the timing of video signals reproduced b y the reproducing heads does not represent rotation phases of the recording heads as the recording heads and the reproducing heads are mounted at staggered positions in the rotation direction of the rotary drum (that is, the recording heads and the reproducing heads are mounted at different mounting angles to the rotary drum).
As described above, this created a problem with the conventional technology. It was difficult to get phase continuity of video signals before and after the editing start point on a magnetic tape through servo control of the rotation of the rotary drum. To cause the phase of vertical synchronous signals of the video signals reproduced by the recording heads before the editing start point to almost coincide with phases of vertical synchronous signals of input video signals to be recorded at time of the editing is not possible in a VTR of the above type because its recording heads are for recording only and reproduction is performed by another heads.